The formation of ordered cross-β amyloid protein aggregates is associated with a variety of human disorders. While conventional infrared methods serve as sensitive reporters of the presence of these amyloids, the recently discovered amyloid secondary structure of cross-α fibrils presents new questions and challenges. Herein, we report results using Fourier transform infrared spectroscopy and two-dimensional infrared spectroscopy to monitor the aggregation of one such cross-α–forming peptide, phenol soluble modulin alpha 3 (PSMα3). Phenol soluble modulins (PSMs) are involved in the formation and stabilization of Staphylococcus aureus biofilms, making sensitive methods of detecting and characterizing these fibrils a pressing need. Our experimental data coupled with spectroscopic simulations reveals the simultaneous presence of cross-α and cross-β polymorphs within samples of PSMα3 fibrils. We also report a new spectroscopic feature indicative of cross-α fibrils.

In many brain areas, such as the neocortex, limbic structures, and auditory brainstem, synaptic zinc is released from presynaptic terminals to modulate neurotransmission. As such, synaptic zinc signaling modulates sensory processing and enhances acuity for discrimination of different sensory stimuli. Whereas sensory experience causes long-term changes in synaptic zinc signaling, the mechanisms underlying this long-term synaptic zinc plasticity remain unknown. To study these mechanisms in male and female mice, we used in vitro and in vivo models of zinc plasticity observed at the zinc-rich glutamatergic dorsal cochlear nucleus (DCN) parallel fiber synapses onto cartwheel cells. High-frequency stimulation of DCN parallel fiber synapses induced LTD of synaptic zinc signaling (Z-LTD), evidenced by reduced zinc-mediated inhibition of EPSCs. Low-frequency stimulation induced LTP of synaptic zinc signaling (Z-LTP), evidenced by enhanced zinc-mediated inhibition of EPSCs. Pharmacological manipulations of Group 1 metabotropic glutamate receptors (G1 mGluRs) demonstrated that G1 mGluR activation is necessary and sufficient for inducing Z-LTD and Z-LTP. Pharmacological manipulations of Ca 21 dynamics indicated that rises in postsynaptic Ca 21 are necessary and sufficient for Z-LTD induction. Electrophysiological measurements assessing postsynaptic expression mechanisms, and imaging studies with a ratiometric extracellular zinc sensor probing zinc release, supported that Z-LTD is expressed, at least in part, via reductions in presynaptic zinc release. Finally, exposure of mice to loud sound caused G1 mGluR-dependent Z-LTD at DCN parallel fiber synapses, thus validating our in vitro results. Together, our results reveal a novel mechanism underlying activity-and experience-dependent plasticity of synaptic zinc signaling.

Here, we present a series of fluorinated cationic reagents that enable rapid arylation of cysteine under mild conditions compatible with proteins and peptides. The highly polarized C–F bond and attractive nucleophile–electrophile Coulombic interactions substantially accelerate cysteine arylation, leading to unusually high rate constants on the order of 100 M–1·s–1 and allowing for equimolar labeling of substrates at micromolar concentrations. The synthetic modularity of this approach promotes the direct coupling of structurally diverse phenol-containing functional motifs to cysteine residues of biomacromolecules with high efficiency. This user-friendly chemistry enables fast bond formation between commonly used bioconjugation partners, thus greatly streamlining the synthetic chemistry workflow, and can be easily developed as convenient kits for chemical biology and medicinal chemistry applications.

The formation of ordered cross-β amyloid protein aggregates is associated with a variety of human disorders. While conventional infrared methods serve as sensitive reporters of the presence of these amyloids, the recently discovered amyloid secondary structure of cross- fibrils presents new questions and challenges. Herein, we report results using Fourier Transform infrared (FTIR) spectroscopy and two-dimensional infrared (2DIR) spectroscopy, to monitor the aggregation of one such cross-alpha forming peptide, phenol soluble modulin alpha 3 (PSM⍺3). Phenol soluble modulins (PSMs) are involved in the formation and stabilization of Staphylococcus aureus biofilms, making sensitive methods of detecting and characterizing these fibrils a pressing need. Our experimental data, coupled with spectroscopic simulations, reveals the simultaneous presence of cross-⍺ and cross-β polymorphs within samples of PSM⍺3 fibrils. We also report a new spectroscopic feature indicative of cross-alpha fibrils.

Supporting information for this article is given via a link at the end of the document.